[Extensions] Don't allow content scripts on the New Tab Page

chrome/test/data/extensions/api_test/content_scripts/ntp/background.js

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function testExecuteScriptInNewTab() {
+  // Create a new tab to chrome://newtab and wait for the loading to complete.
+  // Then, try to inject a script into that tab. The injection should fail.
+  chrome.tabs.onUpdated.addListener(function listener(tabId, changeInfo, tab) {
+    if (tab.url != 'chrome://newtab/' || changeInfo.status != 'complete')
+      return;
+    chrome.tabs.onUpdated.removeListener(listener);
+    chrome.tabs.executeScript(tab.id, {file: 'script.js'}, function() {
+      chrome.test.assertTrue(!!chrome.runtime.lastError);

[karandeepb, 2017/07/18 19:27:00]

I am not up to speed with how different JS types behave with !. Can this check
be made more specific? (Meaning assuming the default value for lastError when no
error is set is null, can we check lastError !== null)

[Devlin, 2017/07/18 20:53:46]

!!x checks that x is not "false-y".  This has tradeoffs vs !== null.  In
particular, it discounts any falsey value, including
undefined
null
0
''
etc

In some cases, that's bad, but in this case, that's actually a good thing.  In
particular, the test of
chrome.test.assertTrue(chrome.runtime.lastError !== null)
would pass, even if chrome.runtime.lastError === undefined.

if there is a last error, then lastError should be something truthy, and this
check is targeting that.

[karandeepb, 2017/07/18 21:06:25]

Acknowledged.

+      chrome.test.assertTrue(
+          chrome.runtime.lastError.message.indexOf(
+              'Cannot access contents of') != -1,
+          chrome.runtime.lastError.message);
+      chrome.test.succeed();
+    });
+  });
+  chrome.tabs.create({url: 'chrome://newtab'});
+}
+
+chrome.test.sendMessage('ready', function() {
+  chrome.test.runTests([testExecuteScriptInNewTab]);
+});